1. Field of the Invention
The present invention mainly relates to an encoder and, more specifically, to an encoder which optically detects positional information of a moving body.
2. Description of Related Art
In recent years, as a scan-type encoder, an encoder has been proposed which moves along with a moving body, and positional information of a scale is detected by, irradiate the scale, which a grating is periodically formed along the movement direction, with irradiation light that is modulated on the basis of a given modulation signal, and then comparing the reflected light or the transmitted light with the modulation signal (U.S. Pat. No. 6,639,686).
Also, as the scan-type encoder, there is a technique which detects the information of the irradiation position of the first light on the moving body, on the basis of a second light which irradiates the first light to the moving body that is a scale for measurement and irradiated to a reference scale or a midpoint monitor that is different from the moving body (PCT International Publication No. WO 07/077,855).